Handheld computers and other handheld electronic devices, such as mobile telephones, PDAs, reading pens, and scanners, are usually controlled by means of one or several buttons or keys, with the aid of which a user issues various commands to the device or inputs information which the device is to use. If there are only a few buttons, controlling the device is usually complicated and time-consuming. On the other hand, if there are many buttons/keys they are usually small in order to only require a small amount of space on the handheld device, which makes them inconvenient to use and increases the risk of pressing the wrong button/key.
U.S. Pat. No. 5,852,434 discloses a device which enables a user to input hand-written and hand-drawn information to a computer while the information is being written/drawn on the writing surface. The device comprises a writing surface, on which a position code is arranged for coding X/Y coordinates of positions on the surface, and a special pen with a writing tip by means of which the user can write or draw on the writing surface. Furthermore, the pen has a light source for illuminating the position code and a CCD sensor for forming an image of the position code. The positional information received by the CCD sensor is transferred to a computer for processing.
WO 99/48268 discloses a handheld device for writing a telephone number and sending the number to a mobile telephone for automatic dialing.